Estimation Of Genetic Parameters Under Optimal And Suboptimal Environments For Body Weight In Chicken Using A Diallel Mating System

Author : M. Gilbert Jeyaruban
Publisher :
ISBN 13 :
Total Pages : 424 pages
Book Rating : 4.E/5 ( download)

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Download or read book Genetic Evaluation and Selection in Egg-laying Poultry written by M. Gilbert Jeyaruban and published by . This book was released on 1992 with total page 424 pages. Available in PDF, EPUB and Kindle. Book excerpt: Estimation of genetic paramenters from a selected population using an animal model was studied along with several problems in optimization of selection response with an acceptable rate of imbreeding in poultry populations using various methods of genetic evaluation, restrictions on selection, mating ratios and population sizes. The genetic parameters for 6 recent generations of a selected commercial egg-laying poultry popuolation were estimated using a derivative free restricted maximum likeihood procedure based on an animal model. The estimated genetic variances for five economically important traits were found to be influenced by the number of generations of data used in the evaluation. This in the evaluation. This finding was examined in a simulation study with different population sizes and different selection intensities for males and females. A normal and a sex-limited trait, both with heritabilities of 0.1 or 0.5 were considered. Estimated additive genetic variance for both the normal and sex-limited trait with a heritability of 0.1 did not show any clear trend as the number of generations of data were increased. But for a heritability of 0.5, the estimated geneticvariances decreased as the number of generations used in the estimation decreased. Use of two generations data led to underestimates of truegenetic variance and use of 5 generations led to over estimates. The exact combination of conditions leading to these biases was not identified and the need for further research was highlighted. The diferences in genetic response and rate of inbreeding were examined by stochasticsimulation of egg-laying poultry selection stocks for traits with heritabilities of 0.1, 0.2 and 0.5 when selecting on estimated breeding values using an individual animal model evaluation (BLUP) or evaluation based on family selecting indexes. The BLUP evaluation gave slightly higher selection responses then the selection indexes, with the differences being almost non-existent at high heritability. But BLUP also gave considerably higher rates then selection indexes. Thus, on the basisof response and inbreeding there seems to be advantage to applying BLUP evaluations for egg-laying poultry stocks. The effects of mating ratio, population size and restrictions on the selecton of close relatives on the selection response and rate of inbreeding were examined by stochastic simulation. Selecton was based on an index comprising 3 economically important traits in egg-laying poultry. The simulation resultsshowed thet population size of around 3000 recorded females and a mating ratio in the range of 1:8 to 1:6 (male:female) would be appropriateto get good selection responses (about $8.5 Cdn. after generation 10) with moderate rates of inbreeding (about 1.2 to 1.5% per generation).